I think some consideration has to be made regarding the audience of these game series migrating to PS3. A game that sells mainly to a hardcore gaming audience is going to fair better than a game that relied on a casual audience when transitioning to the PS3. I think this is why Disgaea 3 and DMC4 faired a lot better than DW6/HSG5 with regards to drop-off in sales compared to their PS2 prequels.
In Disgaea's case, its audience is exactly the type of gamer that would run out to buy a $500 system with next to no games in its first 6 months on the shelf. DMC4 had some of those and a lot of marketing/hype. I think its evident that both the Dynasty Warrior and Hot Shots series have a lot of casual gaming fans as well as some hardcore fans. The problem for both of those series on the PS3 is that those casual fans don't have a PS3 yet and are perfectly content with their DS, PS2, and maybe their Wii.
This is why I have confidence that MGS4 will sell better than DW6/HSG5. While sales of previous MGS games were never as high as the sales of HSG or DW, I don't think it's the type of game that is primarly selling to a casual market. It won't reach MGS3 levels in japan, but its core fans and no doubt stellar advertising should see it to 500k.
On the otherhand, expect massive drop-offs on GT5. A game that DOES largely sell to a casual audience. GT4
rologue sold to roughly 75% of GT4s eventual audience. GT5P was pricier, so it may not have snagged as many Gran Turismo fans, but I can't see GT5 proper doing much better than twice GT5Ps LTD unless the PS3s installed userbase is much higher in Japan before it drops.